sedimentary

Concretion (likely iron-rich sandstone or claystone concretion)

Diagenetic carbonate/iron-oxide concretion; exact mineralogy requires testing

AI-generated identification · may be incorrect

Tan, rounded, irregularly layered specimen with earthy to dull luster and visible weathering cracks. Likely hardness about 3–6 Mohs, depending on carbonate versus silica content; non-cleavable and granular internally.

Identified August 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when minerals precipitated around a nucleus during sediment burial, cementing surrounding sand or mud into a resistant nodule. Such concretions commonly form in relatively young sedimentary deposits, though age cannot be determined visually.

Uses & applications

Primarily a geological curiosity or display specimen; generally no industrial or jewelry value unless unusually shaped, fossil-bearing, or compositionally distinctive.

Geological facts

The concentric, knobby form and contrasting cement-rich layers are characteristic of a concretion rather than a conventional crystalline rock. It may contain a fossil, organic fragment, or mineral grain at its center.

Field identification & locations

Common in sandstone, mudstone, lake, river, and coastal sediments worldwide. Test with dilute hydrochloric acid for carbonate fizz, streak on unglazed porcelain, and inspect a fresh break for sand grains or fossil material.